This is expected, and by design. CSV (and XML) exports are designed to be very generic data preserving formats. They include any dynamic data in the report as a field. All fields will be listed in the header row, where the field name is the name of the text box in the report.
If you need custom formatting such as a header row with report totals, or date of execution, then SSRS CSV export is probably not for you. I'd look at SSIS or writing a custom export application(.exe.) Or you could look at using one of the other export formats from SSRS.